She did not say if the Fed still planned for three rate hikes this year, as it had signaled in December. Nor did she give indications if a hike might come at its meeting in March or in June, as most analysts expect.

While President Donald Trump’s pro-business stance sparked a record-setting rally in equities, he has given scant detail on his policies, giving the Fed limited visibility on the direction of the economy.

“It is too early to know what policy changes will be put in place or how their economic effects will unfold,” Yellen said.

She said delaying rate hikes could leave Fed policymakers behind the curve and lead to quicker rate hikes down the line, which could cause a recession.

Yellen’s rate hike comments lifted the dollar and U.S. Treasury yields, while boosting the S&P financial sector, which rose 0.8 percent. Bank stocks were the top gainers on the S&P and the KBW banking index rose 1.3 percent.

Nine of the 11 major S&P sectors were lower, led by the high dividend-yielding utilities and real estate sectors, both of which were down more than 1 percent.

“While emphasizing the broadening improvements in the U.S. economy, Chair Yellen highlighted the still-uncertain outlook, including on account of possible changes in fiscal policy and ‘developments abroad,’ and thus the importance of a highly responsive monetary policy.” said Mohamed El-Erian, chief economic adviser at Allianz in Newport Beach, California.

At 10:49 a.m. EDT the Dow Jones Industrial Average was down 9.17 points, or 0.04 percent, at 20,402.99, the S&P 500 was down 3.96 points, or 0.17 percent, at 2,324.29 and the Nasdaq Composite was down 9.32 points, or 0.16 percent, at 5,754.63.

General Motors was the biggest percentage gainer on the S&P, rising 3.9 percent after Peugeot-owner PSA Group said it is in talks to buy GM’s European Opel business.